Development of a wall-shear-stress sensor and measurements in mini-channels with partial blockages
Abstract
The design, construction, operation and validation of a wall-shear-stress sensor, and measurements obtained using this sensor in air flows downstream of partial blockages in a mini-channel are presented. The sensor consisted of a hot wire mounted over a small rectangular slot and operated using a constant-temperature anemometer. It was used to investigate flows similar to those within the mini-channels inside notebook computers. The overall goal of the present work was to develop a sensor suitable for measurements of the wall-shear stress in such flows, which can be used to validate corresponding numerical simulations, as the latter are known to be often surprisingly inaccurate. To this end, measurements of the wall-shear stress, and the corresponding statistical moments and power spectral densities, were obtained at different distances downstream of the partial blockage, with blockage ratios of 39.7, 59.2, and 76.3 %. The Reynolds number (based on average velocity and hydraulic diameter) ranged from 100 to 900. The results confirmed the presence of unsteadiness, separation, reattachment, and laminar-turbulent transition in the ostensibly laminar flow of air in mini-channels with partial blockages. The present results demonstrate why accurate numerical predictions of cooling air flows in laptop and notebook computers remain a challenging task.
- Publication:
-
Experiments in Fluids
- Pub Date:
- May 2014
- DOI:
- 10.1007/s00348-014-1734-4
- Bibcode:
- 2014ExFl...55.1734A
- Keywords:
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- Reynolds Number;
- Turbulence Intensity;
- Recirculation Zone;
- Channel Height;
- Blockage Ratio